LABORATOIRE DE PHYSIQUE DES LASERS Photonique Organique et Nanostructures Support de thèse : ANR OLD-TEA Direction de thèse : Alexis Fischer et Azzedine Boudrioua Encadrement : Mahmoud Chakaroun Assistance technologique Jeanne Solard Collaboration: Chii-Chang Chen,National Central University, Taiwan Investigation of photonic properties of self organized nanoparticles monolayers : application to photonic crystal cavities and patterned organic light emitting diodes Getachew-T AYENEW PhD defence : July 8th, 2014

Outline 1.Introduction ► Context ► State of the art ► Our approach 2.Photonic properties of monolayer of opals and inverse-opals ► Numerical study of photonic band gaps ► Numerical study of microcavities ► Experimental approach of characterizing monolayer of opals 3.Nanoparticle based 2D patterning of OLED ► 2D pattering of surfaces ► 2D patterning of OLEDs 4.Conclusion and perspectives 2

3 1D Vertical confinement Top downBottom up Small Mode volume High Q Extended cavity 1. Introduction Context :ANR OLD-TEA Axe 1 Organic Laser Diode : A Threshold-Less Experimental Approach Axe 2 2D lateral confinement Photonic CrystalOpals - Inverse Opals Low threshold organic diode laser 2D DFB lasers Light extraction in OLED Potential Applications

►Photonic properties of monolayer of nanoparticles and microcavities ►New patterning technique using nanoparticles 4 1. Introduction Objectives of the study Self-organized Nanoparticles Photonic crystalsOLED Nanostructuration Photonic crystal laser with defect microcavity 2D-DFB OLDLight extraction in OLED

►Photonic properties of monolayer of nanoparticles and microcavities ►Making nanostructures using nanoparticles 5 1. Introduction Objectives of the study Self-organized Nanoparticles Photonic crystalsOLED Nanostructuration Photonic crystal laser with defect microcavity 2D-DFB OLDLight extraction in OLED

6 State of the art Polymeric solid-state dye lasers resonator Shi et al. Appl. Phys. Lett. 98, (2011) Random lasing Dye doped photonic crystal Kim et al Chem. Mater., 2009, 21 (20), pp 4993–4999 Murai et al, Chemistry LettersVol. 39 (2010), No. 6 p.532 porous photonic film  enhanced stimulated emission  Lasing by randomly dispersing nanoparticles into a gain material multiple scattering highly-efficient low threshold laser Emission spectra of the resonator cavity below and above lasing threshold 2. Photonic properties of monolayer of opals and inverse-opals

► General objective ► Optimal design of planar photonic crystal using nanoparticles ? ► Microcavity ? ► Methodology ► Investigate numerically photonic band gaps in monolayer of dielectric spheres ► Investigate numerically quality factors of microcavities ► Experimental investigation of in-Plane propagation 7 glass General objective/Methodology 2. Photonic properties of monolayer of opals and inverse-opals

Opal without substrate Numerical studies Introduction Structures glass air 2r2r r glass a Inverse opal without substrate Opal with substrate Inverse opal with substrate r a a = period r = radius 2. Numerical study of photonic band gaps

9 2.5 Control parameters Rafractive index (n) for compact arrangement(r/a=0.5) ratio= r/a ( for n = 2.1, TiO 2 )  r/a=0.5, compact structure  r/a< 0.5, non compact structure If no good optical properties for avialable materials n ► Refractive index (n) for compact arrangement of spheres ► n of spheres in opals ► n of infiltrated material in inverse-opals ► Compactness of spheres, r/a ratio ( for n = 2.5, anatase TiO2) ► r/a=0.5, compact spheres ► r/a < 0.5 non- compact spheres ► r/a ratio determines the filling factor 2. Numerical study of photonic band gaps

Parameters Rafractive index (n) for compact arrangement(r/a=0.5) ratio= r/a ( for n = 2.1, TiO 2 )  r/a=0.5, compact structure  r/a< 0.5, non compact structure If no good optical properties for avialable materials ► Propagation direction of the incident field with respect to the crystal ► Г M ►  K ► Polarisations of the field ► TE ► TM E TM TE K K E 2. Numerical study of photonic band gaps

►Boundary conditions ► Perfectly matched layer (PML) ► Periodic Introduction to simulation Simulation condition ► 3D finite-difference time-domain(3D-FDTD) 2. Numerical study of photonic band gaps Top view Cross section

►Photonic band gap►Gap maps 12 Photonic band gap(PBG) and construction of gap maps PBG n=2.2 n=3 n=2.1 PBG n=1.5 Photonic gapmap Transmission spectra 2. Numerical study of photonic band gaps

►Gap maps ► Different polarizations ► TE ► TM ► Different directions of propagation ►  M ►  K 13 Photonic band gap(PBG) and construction of gap maps 2. Numerical study of photonic band gaps

PBG 14 Inverse opals without substrate Region for TE polarization r/a=0.5 n=2.5 TiO 2 (n=2.5) ►PBG exists for a wide range of refractive indices ►PBG exists for a wide range of compactnesses ►For n=2.5, Largest gap to mid-gap ratio for r/a=0.4, (TE) ΔfΔf f Width of gap = gap-mid-gap ratio= Δ f/f 2. Numerical study of photonic band gaps

►Opals without substrate exhibit PBGs for different compactness 15 n=2.5, TiO 2 Opals without substrate 2. Numerical study of photonic band gaps

►First conclusion- monolayer of inverse opal offers larger gap-to-midgap ratio 16 г M-TE Opal or inverse opal ? 2. Numerical study of photonic band gaps

►Losses to glass substrate ►No PBG for low ref. index materials ►We have to choose higher index materials 17 r/a=0.5 n=2.5 ►PBG observed when using non- compact spheres ►Overlap of TE mode for non-comact spheres TiO 2 (n=2.5) Substrate effect : inverse-opal 2. Numerical study of photonic band gaps

►Losses to glass substrate as r/a is lower ►More compact spheres favorable 18 n=2.5 Lossy region glass Substrate effect : opal 2. Numerical study of photonic band gaps

►Opals: as the spheres are more compact n eff increases  less loss ►Inverse opals: as the spheres are more compact n eff decreases  more loss 19 n=2.5 ►PBG observed when using non- compact spheres n=2.5 Substrate effect : effect of compactness on losses 2. Numerical study of photonic band gaps Compact high n eff Non compact low n eff Less compact smaller filling factor More losses compact low n eff Non compact high n eff More compact More losses larger filling factor

20 ►PBG observed when using non- compact spheres Substrate effect : effect of compactness on losses 2. Numerical study of photonic band gaps Compact high n eff Non compact low n eff More losses compact low n eff Non compact high n eff More losses

►Conclusion ► Structures without substrate exhibit PBGs for wide range of refractive indices and compactness ► Generally inverse opals have larger photonic bandgap width ► Structures with substrate have losses for lower refractive index materials ► Considering n=2.5, lower compactness in inverse opals and higher compactness in opals result in lower losses to glass substrate ► Inverse-opal with lower compactness on glass substrate seems to be a good compromise between the losses and the width of PBG ►Thus microcavities designed in non-compact sphere inverse-opals are expected to have better confinement ► Calculation of quality factors is necessary to optimize the optimum r/a value for a given refractive index 21 Conclusion 2. Numerical study of photonic band gaps

► General objective ► Optimal design of planar photonic crystal using nanoparticles ? ► Microcavity ? ► Methodology ► Investigate numerically photonic band gaps in monolayer of dielectric spheres ► Investigate numerically quality factors of microcavities ► Experimental investigation of in-Plane propagation 22 glass General objective/Methodology 2. Photonic properties of monolayer of opals and inverse-opals

► Investigation with respect to ► Various cavity geometries ► The r/a ratio ► with and without substrate (effect of the losses) 23 The Quality factor investigated with respect to: - with respect to the r/a ratio -the cavity type H1 L5 L3 H2 Microcavities ►Fixed refractive index n= 2.5 ►Defects in the periodicity monitor source 2. Numerical study of microcavities

►Cavity resonance in the PBG ►Significant resonant peaks observed for non-compact arrangement Microcavities in inverse-opals 2. Numerical study of microcavities

►Quality factor optimized when r/a < 0.45 ►The presence of glass substrate reduces the quality factor ►The maximum of the Q-factor is obtained for 0.3 < r/a < Microcavities in inverse-opals 2. Numerical study of microcavities

26 H2 Higher refractive index values needed in opals to achieve a resonance: (n~4 realistic?) ► The inverse-opal arrangement is more favorable for microcavities Higher refractive index of dielectric spheres needed in opals to have a resonance With the presence of glass substrate, the refractive index of the spheres needed is not feasible with available materials Microcavities in opals 2. Numerical study of microcavities n=4 n=3.2

►Highest Q-factor(~300) obtained for non-compact spheres in inverse-opals. ►With a glass substrate the Q factor is limited to Q~200 ►Glass substrate reduces Q-factors ►Micro-cavities in opals require refractive index larger than n=3.2 which is hardly feasible ►The literature presents much higher Q-factor in conventional Phc Slabs. 27 Conclusion on Microcavities 2. Numerical study of microcavities

► General objective ► Optimal design of planar photonic crystal using nanoparticles ? ► Microcavity ? ► Methodology ► Investigate numerically photonic band gaps in monolayer of dielectric spheres ► Investigate numerically quality factors of microcavities ► Experimental investigation of in-Plane propagation 28 glass General objective/Methodology 2. Photonic properties of monolayer of opals and inverse-opals

29 ►Angle resolved reflection or transmission of multilayer opal in optical regime Reflection spectra Simple fabrication method of monolayer of micro-spheres and simple in-plane transmission characterization ? Maybe – our technique ►In-plane transmission properties of monolayer of periodic spheres in terahertz regime Sphere diameter= 8mm Soda lime glass spheres, n= Towards experimental study of in-plane propagation of opal monolayers State of the art : characterization of array of dielectric spheres ►In-plane transmission properties of monolayer of periodic spheres in optical regime micrometer-sized spheres mechanically arranged under a scanning electron microscope figure

► Objectives ► Measure of the In-Plane transmission spectra as a function of ► Polarization (TE, TM) ► Crystal direction (  M,  K) ► Problem ► Arrangement of spheres – presence of multiple domains ► Several directions are probed at the same time ► Method ► Fabrication of a single domain monolayers ? ► Characterization of single domain ? 30 In plane transmission spectra characterisation of Monolayer dielectric spheres in optical regime  Problems Many crystal domains in self assembled monolayer of spheres Nanoparticles too small to be manipulated 2. Towards experimental study of in-plane propagation of opal monolayers Problem and method transmitted Direction of propagation

►Fabrication ► Fabrication of micro-hexagons ► Micro-hexagon to force nanoparticles in ordered manner ► Dimension calculated for given nanoparticle diameter 31 In plane transmission spectra characterisation of Monolayer dielectric spheres in optical regime  Problems Many crystal domains in self assembled monolayer of spheres Nanoparticles too small to be manipulated ►Characterization ► Waveguides ► In- and out-coupling 2. Towards experimental study of in-plane propagation of opal monolayers Approach: single domain samples and charaterization Microheaxgons Different orientations with respect ot the directionof propagation

32 10µm 2. Towards experimental study of in-plane propagation of opal monolayers Preliminary experimental results: Fabricated waveguides

► Video : 33 sample 2. Towards experimental study of in-plane propagation of opal monolayers Preliminary experimental results: Deposition of nanoparticles

►The diameter of the microneedle is too large as compared to the size of the micro-hexagon ►Nanoparticles not in the target area : 34 ►1.5µm spheres used for optimization of the process 2. Towards experimental study of in-plane propagation of opal monolayers Preliminary experimental results: Deposition of nanoparticles Perspective : Use microchannels to inject the solution into the hexagonal hole for better contro

35 2. Towards experimental study of in-plane propagation of opal monolayers Approach: Characterization

36 2. Towards experimental study of in-plane propagation of opal monolayers Conclusion and perspectives on experiments ►Conclusion ►... ►Perspectives ► Buried waveguide ► Microfluidic for... ►Image guide enterré ►Microfluidique ►Reference article

37 2. Towards experimental study of in-plane propagation of opal monolayers Conclusion and perspectives on opals and inverse-opals ►Numerical investigation on opals and Inverse opals ► Inverse-opals exhibits larger PBG ► …. ► Microcavities ►Towards experiments on opals ► Proposition of an experiments to characterize in-plane progpagation of single domain opals ► Microhexagons ► waveguide ►...

►Photonic properties of monolayer of nanoparticles and microcavities ►Making nanostructures using nanoparticles OLED Nanostruturation Objectives of the study Self-organized Nanoparticles Photonic crystalsOLED Nanostructuration Photonic crystal laser with defect microcavity 2D-DFB OLDLight extraction in OLED

39 ►Laser ablation ►Projection ►MicroLens ► microsphere deposited every time patterning is made State of the art: Microsphere based lithography 3. 2D nanostructuration of OLED

40 OPTICS EXPRESS / 2005 / Vol. 13, No. 5 Nano Letters, 2002, 2 (4), pp 333–335 Thin Solid Films 492 (2005) 307 – 312 ► E-beam lithography ► Nanosphere lithography ► Inprint State of the art: 2D patterning of OLEDs 3. 2D nanostructuration of OLED

►Objectives ► Patterning OLED ► Light extraction requires size about µm ► 2D DFB laser for emission at l=620nm requires lattice= 250nm ► Investigate alternate techniques ►Issues ► E-beam ► Time consuming ► Expensive ►Method ► Principle Photolithography using NP ► Analysis ► Simulations ► experiments OLED Nanostruturation Objectives of the study

42 ► Nanoparticle based reusable photolithographic mask ► Reproducing the pattern ► Photo mask madewith NP ► Light exposure ► Patterning of photoresist Principle of the technique 3. 2D nanostructuration of OLED

►P rocess paameters 43 Glass UV ITO Photoresist Experiment : The process 3. 2D nanostructuration of OLED

► Large area microsphere-thin-film on the substrate cm 1.7cm  Microsphere mask ► Periodically arranged monolayer of spheres - sometimes multiple domains in the crystal Results 3. 2D nanostructuration of OLED

3.4 Results and discussions  Microstructured photoresist 1µm ► Made by 2.34 µm mask 3. 2D nanostructuration of OLED

► Reduced period Results and discussions ►Periodically arranged monolayer of spheres - sometimes multiple domains in the crystal  Micro-ball lens and phase-mask effects On different samples On the same sample ► The phase-mask effect is clearly dimonstrated ► Unreduced period 3. 2D nanostructuration of OLED

47 Micro Lenses Phase mask: Period of pattern equals period of microspheres Period of pattern is half of period of microspheres ► Nanoparticle based reusable photolithographic mask Simulation 3. 2D nanostructuration of OLED

►Lattice less than 750nm and hole diameter less than 450 nm Results and discussions ►Periodically arranged monolayer of spheres - sometimes multiple domains in the crystal  Micro-ball lens and phase-mask effects ►Phase-mask effect not observed for microsphere sizes of 800nm and 1 μm 3. 2D nanostructuration of OLED

►Micro ball-lens ► focal length ► Numerical aperture ►Phase mask properties ► Transmitted angle 49 Analysis 3. 2D nanostructuration of OLED

OLED Red OLED Green OLED 3. 2D nanostructuration of OLED Sketch of the OLED substrate

Results and d discussions ►Periodically arranged monolayer of spheres - sometimes multiple domains in the crystal  Micro-OLED Characterization 3. 2D nanostructuration of OLED

► Micro -OLED sizes = 1.27µm ► Method compatible with OLED operation Results and discussions  Micro-OLED Characterization ► This technique is advantageous over similar techniques like e-beam lithography 3. 2D nanostructuration of OLED

► Small spectral modification of emitted light as compared to large area OLED ► Under normal incidence ► Perspectives / ► Measurements for other angle of incidence ► Edge emission ► Smaller patterns Results and discussions  Micro-OLEDs Characterization 3. 2D nanostructuration of OLED

►Cheap, simple method to pattern 2D surfaces on large area ►The patterning method is compatible with OLED depostion Conclusion and perspectives on OLED nanostructuration 3. 2D nanostructuration of OLED  Conclusion  Perspectives ►Lower wavelength exposure (<450nm) to increase the resolution of this lithography process ► Deep UV photoresist ►DFB lasing can be achieved by appropriate design of the lattice constant ►The method can be applied to make periodic textures in performance enhancement of opto- electronics devices

55 ► Light extraction ► DFB lasing ► Light extraction 3.5 perspectives Conclusion an perspectives UV light 193nm Smaller lattice (250nm)

56 4. General Conclusion ►Photonic properties of Monolyaers of opals ad inverse opals ► … ►OLED 2D nanostructuration ► ….. ► … ► ….

Thank you for your attention

58 Conferences and papers ►Paper 1 ►Paper 2 ►Paper 3 ►Conference 1 ►Conference 2

59 Conclusion an perspectives ►Application of Nanoparticles photolithography ► Patterning surface with metal ► SERS ► Molecules detection ► OLED efficiency increases via Pasmonic resonance

60

gjhgfh ►State of the art ►Opal, inverse, compact non c ►fgfg 61 State of the art ►Fabrication Non- compact spheres ►Inverse opal : sol-gel infiltration 2. Towards experimental study of in-plane propagation of opal monolayers 2.12 State of the art : fabrication and characterization ►Monolayer of PS dielectric spheres  Fabrication

►Filling fraction ► The filling fraction(ff) in hexagonal lattice of monolayer of spheres of spheres of radius “r” and lattice constant “a” is : ►Effective refractive index (n eff ) ► Opal, ► Inverse-opals, ►Impact on losses ► As n eff is smaller, there will be more leakage to the substrate ► In opals, as r/a is low, there will be more leakage ► In inverse-opals, as r/a is high, there will be more leakage Analysis of the results 2. Photonic properties of monolayer of opals and inverse-opals r a Sketch of leakage modes

a.Opals a.Inverse Opals 63 What kind of Photonic crystals from nanoparticles?  Small photonic badgap  Improved photonic badgap What else?  Light extraction in OLEDs: surface roughness  Suppression of the guided mode

How can we make inverse opal PCs? 64 Sol-gel calcination,or use solvent Bottom up approach  Several ways to make nanoparticles

Major tasks: ►Simulation to get PBG -optimum index contrast & lattice constant (b/n air and infiltrated material) kind of material (ZnO,TiO2,SiO2,,,,) diameter of nanoparticles ►Nanoparticle synthesis and self-assembly( in collaboration with N. Jouini, LPMTM) ►Sol-gel infiltration and calcinations to get inverse opals ( collab. L. Znaidi, LIMHP, prof. Chii-Chang Chen,NCU) ►Realization of cavity ►Characterization photonic crystals ► reflectance, transmittance ►OLED deposition ►Device characterization ► Spectral and coherence 65

Current work … ► Literature ( on self assembly,sol-gel,laser physics…) ► Simulation of PBG: o PWE, FDTD And in January 2011: experiments on self-assembly of nanoparticles in clean room 66

Thank you 67

► Fabrication will be more complicated (eg. Reactive ion etching) 68 With the presence of glass substrate, the refractive index of the spheres needed is not feasible with available materials

69 1.Introduction  Organic luminescence (OLEDs, organic lasers)  Photonic crystals  Making nanoastrucutrures  Self –organization principle  State of the art: how nanoparticles are used  Our approach of using nanoparticles 2. Monolayer of nanoparticle based photonic crystals  Transmission spectra Effect of refractive index Effect of compactness of Spheres Substrate effects  Cavity quality factor  Experimental chachterization Fabrication of monolayer of spheres Charcterization mechanisim of monolayer of spheres 3. Monolayer of nanoparticles to make Microstrcutures  Principle and theory  Experiment Making nanostrucutres Making Micro-OLEDs 4. Conclusion and Perspective

What is nanoparticle ? ►One of dimensions in the order of 100 nm or less nm ►a bridge between bulk materials and atomic or molecular structures. ►behave very differently compared to bulk material wave properties of light are important capillary force more important than gravitational force 70

Why Nanoparticles based?  short time-to-market and low-cost  easy processing technology What kind of nanoparticles ?  Polystyrène, PMMA, SiO 2,,,, 71

Using photonic crystals:  Photonic crystals  Defect cavity on PC o Modify spont. Emission 72  narrow-linewidth lasers  Low laser threshold  Appropriate defect cavity : λ λ Δλ No liberté to propagate

Motivation & Objective  Motivation  OLED current density is low (< 1A/cm²) 1.low threshold current density in organic lasers is compulsory ► Large spectral line width in emission of organic materials ( >40nm) 1. Low extraction efficiency of generated photons in OLEDs  Objective:  Design and realization of Organic Laser diodes embedded in photonic crystal cavities ► To make photonic structure based on nanoparticles  bottom-up approach ► Defect cavities in photonic crystal ► Modification of the spontaneous emission  improve » laser threshold reduction »Spectral line width reduction 73

The autorgani….. ►The autoorganisation 74